Process and apparatus for dewaxing petroleum oils



Dec. 9, 1941. D, G. BRANDT PROCESS AND APPARATUS FOR DEWAXING PETROLEUM OI Filed May l1, 1958 y HVIQ Patented Dec. 9, 1941 PROCESS AND APPARATUS FOR DEWAXING PETROLEUM OILS David G. Brandt, Westfield, N. J., assigner to Cities Service Oil Company, New York, N. Y., a corporation of Pennsylvania Appucation May 11, 1933, serial N0. 207,231 9 claims. (ci. 19e-1s) This invention relates to a process for dewaxing petroleum oil stocks, and more particularly to a process in which a liquid normally gaseous hydrocarbon is used as a solvent and diluent.

A large number of different processes have 670,066, filed May 9, 1933, for an improvement in the Art of dewaxing oils. In accordance with the disclosure of that application, the oil stock to be dewaxed is passed through a series of chilling chambers through which the diluted oil mixture is passed in series and portions of the liquid propane vaporized in each chamber to chill the oil mixture and precipitate the Wax content thereof. In this process provision is made for introducing precooled propane into the oil mixture passing from one chilling chamber to the other, in order to make up for the vaporized propane and aid in chilling the oil mixture.

Dewaxing processes which involve the step of vaporizing a portion of the diluent in contact with the mixture being chilled have been reason- F ably successful, but the Vaporization produces an intense agitation of the mixture, so that crytsal growth is prevented, and in some cases crystals which have been formed are broken up into smaller units. Oil stocks containing small crystals are much more diflicult to handle in the Wax separation stage than are stocks containing large crystals.

Accordingly, the primary object of the present invention is to provide an improved process in which the chilling operation to precipitate the Wax content of the oil is carried out under conditions particularly adapted to the formationv of large crystals and the maintenance of such crystal structures as are formed.

In general, the process of the present invention includes the steps of completely dissolving the oil stock to be dewaxed in a liquefied normally gaseous hydrocarbon such as propane, cooling the solution by indirect heat exchange to a temperature only slightly above the pour point of the oil stock or the point at which wax precipitation would commence, passing the cooled solution into a wax precipitating chamber into which sufficient precooled chilling agent including liquid propane is injected to effect the desired chilling of the mixture and precipitation of the Wax content thereof, said injected chilling agent being comprised at least in part of a cold DIG- pane solution derived from the Washing of the wax eventually obtained in accordance with the features of the process.

The process of the present invention comprises other features, objects, and advantages which will be apparent to those skilled in the art from the following more detailed description thereof, taken in connection with the accompanying drawing in which the single figure is a diagrammatic ow sheet of an apparatus particularly adapted for carrying out the features of the improved process and in which certain of the elements of the apparatus are shown in vertical position.

The petroleum oil stock to be dewaxed which may be an overhead Wax distillate or a long residuum, and preferably relatively free from asphaltic constituents is preferably diluted with at least 30% to 50% of a liqueiied normally gaseous hydrocarbon such as propane and completely brought into solution. This operation may require heating to a temperature of from to F.

The oil stock to be dewaxed is introduced into the apparatus shown in the drawing through a line l, and passed into a mixer 2 in which it is dissolved in liquid propane introduced through a line 3. The resulting solution is passed through an indirect heat exchange chamber or tower 4 where it first passes in heat exchange with a cooling liquid such as Water conducted through the coil 6, and then in heat exchange with a colder fluid such as the cold dewaxed oil produced by the process which is conducted through a heat exchange coil 8. The solution of oil stock passed through the chamber 4 is preferably cooled therein to a temperature just short of the temperature at which Wax would start to precipitate, so that no Wax is precipitated on the coils or the Walls of the chamber 4.

The cooled solution of oil stock is conducted from the chamber 4 through a valved line I0 into a chilling chamber I2, wherein the oil 'stock passes through a series of chilling compartments separated only by baffle plates so that the oil stock passes in succession through the compartments. The oil mixture introduced into the chilling chamber l2 is preferably chilled to progressively lower temperatures, as it passes through the chamber by introducing an increment of precooled liquid propane from a plu- 'in eachA compartment of the chamber.

.other suitable means.

rality of valved intake pipes I4 distributed along the chamber. The propane or other chilling agent injected from each of the pipes I4 is preferably introduced into the side of the chamber through an injection type of nozzle which prevents shock chilling by creating a flow of oil mixture past the nozzle and by producing a gentle circling or eddying action in the oilmixture This insures thorough mixing of the injected cold chilling agent with the oil solution and prevents shock chilling of the oil, andby thetimethe` oil removed from the chamber usually comprises about wax, 25% oil, and about 50% of propane diluent. A considerable proportion of diluent is mixed with the slurry in the line 34 and the resulting mixture introduced into a mixing chamber 36 Where a more thorough mingling of the constituents is accomplished by means of a rotary mixing element mounted inthe chamber 36. The diluted wax slurry is conducted from the chamber 36 through a line 38 into a Wax separating chamber 40 which may be of similar y construction to that of the chamber 20.

has passed through the chamber, its wax; content will have been completely precipitated to the extent desired to produce a stockrofv vdesiredlow pour point. The chilling effected in the chamber I2 may be suicient to superchill the mixture to a suiiiciently low temperature forseparation of the precipitated wax. A temperature, of minus f.,

40 to minus 60 F. is sunicient for most'petrole'` lubricating oil stocks.

The cold mixture containing the precipitated wax is Withdrawn from the chilling: chamber I2 through a valved line I6, passed into a line I8,

and conducted into a wax separa-ting. chamber 20. This wax separating chamber is preferably constructed like the separator shownV in the drawings of the4 pending `application Serial No. 6,70,- 066, referred to above. The separating chamber shown in this pending application is a jacketed chamber inzthe jacket of which liquid propane is-vaporized to maintain a low temperature. The chamber itself is provided With a plurality of vertically spaced trays which slope toward the center of the chamber and which have centralopenings for the passage of settled wax. The trays are alsoof such a size that afree space is left between their outer edges and the inside wall of the separator for the upward passage `o1 separated4 oil solution. Provision is made for introducing oil mixture containing precipitated Wax `at a vpoint above each tray and near the center 'of the chamber so that the space between adjacent trays comprises amore or less individual settlingzone. The settling, chamber is also pro.- i'

lwhile the settledv Wax slurry is removed fromf the bottom ofthe chamber byY a gear pump or In any case, the wax is settled; out inthe, chamber 20, andthe wax-free oil;in. solution in the'liquid propane is withdrawn from the chamber through a line 22 and forced Vbyrymeans ofA a pump. 24,v and a line 26 through vthe; cooling coil 8,mounted in the lower part of :the cooling chamber 4, where the cold dewaXed ,oillsolution is used as a cooling medium.

.The pressure in the chamber I2cmust be main- .:tained sufficiently high to prevent yvaporization -of any of the propane at the highest temperatures of any ofthe materials therein. The pressure may beconsiderably reduced in the line I6,

Ybut. suicientpressure shouldy be'` maintained to prevent vaporization of any of. theY diluent and provide-for the iowwof the oil mixture into the chamber 20, and-the oil; solution throughout the line22.. A superatmospheric pressure of from I0 to 251bs.isisufcient inthe chamber 2,0.

The `wax slurry: separatedV out ini the chamber n2li-.is removed .tromlthe conical bottom of the chamber-through aline 28v andlpassed'by means "f ai-pump 3`0'- and-'aline 32 intoa line 34wnere 'it -i-s finixed with-cold -xiiluentl-Therfwax slurry .an extremely low temperature and therefore suitableas a. direct coolingmedium for the precipitationof. Wax in the chamber I2. In fact thismixture maybe utilized as the entire chilling means vfor precipitating wax in this chamber in accordance with the'ieaturesof the present invention, andI it may be introduced through each line-|4.

The wax. slurry separated4 outintheseparating chamber 40 iswthdrawn from the conical bot- `tomrthereof through avalved line 56 and passed by means of ai pump V52 and a line-54 into, a

mixer 56 similar in construction to the mixe-1236.

The wax slurry removed from the chamber 40 contains about r70%. of propane, 25% of wax, and about 5% of oil. This mixture is further diluted withA extremely cold liquid propane: introduced intothe line 54 from a line 58 and thoroughly mixedr with the slurryinA the mixer.

The diluted wax: slurry is conducted: from the mixer 56 into anal Wax; separating chamber 60 from whichthe-separa-ted wax substantially .free of oilv isremoved through a valved 1ine62. The chamberl 6011s constructed the same as the chamber 20.

t The cold wash solution comprised largely of propane-v and a small proportion of oil is passed fromithe chamber 60- by' the line 34: and used as the cold diluent for mixing with, the wax, slurry withdrawn from the chamber 20.

The propane or other `liqueiied normally gaseous hydrocarbon tov be used in theprocess may ,befintroduced into the systemthrough a line 64,

.passed through aline 66, a condenser 68 anda line l0; into a liquidv propaneV storage tank 12. The propane stored in the` tank 1-2 is usually maintained atvatmosphericA temperature and at a, suncient pressure` to maintain the propane in the liquid state. The cold propane usedy `for precipitatingA the wax content. of the oil and4 for rwashing the separated ,wax' slurry is obtainedfby passing,v liquid propane from the storageta-nk 'I2 through lines 14 and coolers'IiG, ',intoa propane ashchilling chamber 18. The propane `is chilled yby reducing` thel pressure: up'on` the introduction of the propane intoVV the chamber TB, so that a portion of the propane isvaporizedand theremaining portion is retained in the liquid state and chilled. to the desired low temperature. 4

, The propane vapors formed-inV the' chamber 'I8 are removed?. through azvalvedline- 80, passed Ythrough coolers-4 'IIi` invvindirect ,heat exchange with the." liquid propane from the storage tank f'Ii2-`,.V and' then. passed through a" 1ine-482 to a vac,- .uunrpump and compressor 84; Thevaporiza -tiongin' the chillen-'machins botlr the liquidi. and

vaporous' propane, so that the relatively cold vapor conducted through the coolers 'I6 may be effectively utilized in cooling the liquid propane owing to the chamber 18. Any desired pressure or vacuum may be maintained in the chamber I8 by means of the valve in lines 80, and the vacuum pump 84, so that the propane may be cooled to any desired low temperature of from minus 55 to minus 85 F.

The propane vapors picked up by the compressor 84 are placed under a high pressure and passed through the line E6, condensed in condenser 68, and the condensate is conducted through the line IB into the propane storage 12.

The extremely cold liquid propane produced in the chamber I8 is withdrawn therefrom through a line 86, by means of a pump 83, and forced through a valved'line 9B into the connecting lines I4 which are utilized for injecting the cold propane into the chamber I2 in the manner described above.

Cold liquid propane used for washing the wax slurry in chambers E!) and 4B is supplied from the valved line 58, as described above, which line connects directly into the line 9S.

lAfter the wax has been precipitated in the chamber I2, the resulting mixture may be further chilled in order to provide a suitable low temperature for wax separation by vaporizing a portion of the propane diluent under reduced pressure. This step may be effected by passing the mixture from the line IB through a Valved connecting line 92 into a flash chiller 94 where a suitably 10W pressure is maintained to eiect the desired vaporization of propane and consequent chilling of the mixture. The vapor space of chamber 94 is connected with the low pressure or vacuum line 80 by means of a valved connecting pipe 96. The degree of pressure or of vacuum maintained in the chamber 94 is controlled by means of the valve in the line 96. The chilled mixture is Withdrawn from the chiller 94 through a valved line 98 and a pump Iilll and forced through the line I8 into the wax separating chamber where the wax is separated in the manner described above.

Where the oil mixture can be chilled to sufficiently low temperatures in the chamber I2 without diluting the mixture excessivelyt'f the flash chamber 94 need not be used, but this chamber provides an effective means for lowering the temperature of the mixture containing the precipitated Wax, so that a sufliciently low temperature mixture is provided for the wax separation operation. This supercooling of the mixture containing the precipitated Wax Will prevent the re-solution of wax from any slight rises in temperature which may occur during the separation operations.

The entire chilling in the chamber I2 is preferably effected with cold wash liquid from the chamber 4D, but where this is insufcient, or for other reasons, it may be supplemented with cold solvent from flash chiller 58. All parts of the equipment in which low temperatures are involved are understood to be suitably insulated.

While the process of the present invention has been described in connection with the use of propane as the diluent, it is to be understood that other oil solvents of low specic gravity may be employed which are relatively poor solvents for petroleum waxes. Propane and other liqueed normally gaseous hydrocarbons having molecular weights below that of pentane are particularly suitable for the process.

Having thus described the invention in its preferred form, what is claimed as new is:

1. In the process of dewaxing petroleum lubricating oil stocks in which the oil stock to be de- Waxed is diluted with liquid propane in sufiicient quantity and at a temperature adapted to completely dissolve the oil stock and provide a solution which will be fluid and readily handled at temperatures as low as the point of wax precipitation, the improvement which comprises chilling the solution by passing the same through a series of connected enlarged chilling zones in each of which an extremely cold liquid diluent is introduced and mixed with the diluted oil mixture, maintaining the materials in said series of chilling zones at a sufficient pressure to prevent vaporization of any of the propane, introducing the cold diluent into each of said zones in a jetting action adapted to cause only gentle eddying currents in each of said zones to effect equilibrium between the oil mixture and the introduced dilutent therein without shock-chilling the oil, said diluent being introduced in suflicient quantity into said zones to precipitate the wax content of the oil desired to be removed therefrom to give a wax-free oil of predetermined pour point, separating the precipitated wax from the resulting chilled mixture, washing the separated wax with extremely cold liquid propane and utilizing the resulting wash liquid as the cold diluent introduced into said chilling zones.

2. The process of dewaxing petroleum lubricating oil stocks as defined by claim l in which the precipitated wax is settled from the chilled mixture containing the same to form a wax slurry, mixing a substantial proportion of a diluent comprising cold liquid propane with said slurry, and settling the resulting mixture to recover a solution comprising propane and oil Washed from said wax slurry.

3. The process of dewaxing petroleum lubricating oil stocks as defined by claim l in which the precipitated wax is settled from the chilled mixture containing the same to form a wax slurry, mixing a substantial proportion of a diluent comprising cold liquid propane with said slurry, settling the resulting mixture to recover a solution comprises propane and oil and a second wax slurry, separating out said second wax slurry and mixing therewith a substantial proportion of extremely cold liquid propane, separating a substantially oil-free wax from the resulting solution of propane and oil, and mixing said last named solution with the wax slurry formed in the original wax settling step as said cold liquid propane diluent.

4. In the process of dewaxing petroleum lubricating oil stocks in which the oil stock to be de- Waxed is diluted with a liquefied normally gaseous hydrocarbon which is liquid at low dewaxing temperature in sufficient quantity and under suitable conditions to completely dissolve the oil u stockv and provide a solution which flows readily at temperatures as low as the pour point of the oil stock, the improvement which comprises chilling the oil solution with a chilling medium and precipitating the entire wax content thereof desired to be removed therefrom in an enlarged elongated chilling zone in which a sucient pressure is maintained to prevent vaporization of the liquid normally gaseous hydrocarbon, effecting the chilling of the oil solution in` said zone by introducing thereinto at spaced points therealong a cold chilling medium, passing the resulting mixture from said zone into a wax settling vented.

'slurry and a solution containing' a relatively large. proportionof liquefied normally gaseous hydrocarbon and a relatively small proportion of oil, and utilizing said solution asv the chilling medium for effecting the precipitation of wax in said chilling zone by intimately mixing the solution with the oil stock introduced thereinto under conditions such that: vaporization ofthe liquefied normally gaseous hydrocarbonV is pre- 5.A 'Ihe process of' dewaxng. petroleum` oil stocks as dened by claim 4 in which thev second Wax slurryV is mixedy with: al.substantial proportion. of extremely cold liquefied normally; gaseous hydrocarbon and' subjected to a' settling 'operation, settling the'wax from the resulting solution comprised main-lyfofA said hydrocarbon. and. va small proportionV of oilv stock, and utilizing said solution as the' liqueii'ed normally gaseous hydrocarbon for mixing with the.y wax slurry formed inthe first settling. operation.

6. An apparatus forfdewaxing petroleum lubricating oil stocks. which comprises a; chilling chamber for precipitating wax in anl oil solution introduced thereinto, said chamber comprising a series of relatively llarge interconnecting compartments each ofr which is provided with an injectionmeans, a wax settlingY chamber for settling precipitated wax from a mixture' containing the same, a wax washing chamber, means for introducing an oil solution to -be dewaxed into said chilling chamber, means for passing an oil mixture containing precipitated wax from said chilling chamber into said wax settling chamber, means for passing Wax slurry into said Wax washing chamber, means for introducing 'a cold diluent washing liquid into said wax washing chamber,

and means for passing cold wash liquid from said .wax washing chamber and for introducing itv into each compartment of. said chilling chamber as the chiling medium for precipitating wax. in the oil solution introduced 'into the chilling chamber.

7. In the process of dewaxing petroleum lubri' A Veating oil stocks in which the oilv stockl to be de- Waxed is diluted with a liquid normally gaseous hydrocarbon which is liquid at. Ylow dewaxing temperatures in sufficient quantity and. .at a temperature adapted to completely dissolve the oil'stock and providea solution which will be iiuid and readily handled at temperatures as. low as the pour point of the stock, the improvement whichcomprises chilling'the solution whilepassing the same through a series of connected. enlarged chilling zones in an enlarged chamber by separately'introducing into each zone an extremely cold vliquid'dil'uei'it which is mixed directly with the oil mixture in'said zones, maintaining the materials in said enlarged chamber under sufcient pressure to prevent .vaporization ofv any of said liquid hydrocarbon, introducing. the cold diluent into each of said zones in a jetting action adapted to eiect only gentle eddying currents in said. zones thereby bringing the'diluent and oil mixture into-contact and temperature equilibrium in each of said zones, the cold diluent being introduced into each zonev in such a manner as to avoid shock-chilling of the oil but in such quantity as to crystallize the wax content of the oil desired to be removed therefrom by the time the oil mixture has passed through said series of zones, separating the crystallized wax from the resulting chilled mixture, Washing the separated wax with extremely cold liquid normally gaseous hydrocarbon, and utilizing the resulting Wash liquid as the cold diluent for eiecting the chilling of the oil mixture in said series of chilling zones.

8. The process of dewaxing petroleum lubricating oil stocks as deiined by claim l in which said series of enlarged chilling zones are contained in an enlarged chamber divided by baflles forming said zones, and in which the oil mixture iiows past said baflies in advancing through said series of zones.

9. In the process of dewaxing petroleum lubricating oil stocks in which the stock to be dewaxed 'is diluted with a liquid normally gaseous hydrocarbon which is liquid at low dewaxing temperatures in suiiicient quantity and under suitable conditions to completely dissolve the oil stock in the hydrocarbon diluent and provide a solution which iiows readily at temperatures as low as the pour point of the stock, the improvement which comprises introducing the diluted oil mixture into the top of an elongated chilling zone and owing the oil mixture therethrough over a plurailty of spaced baffles to the bottom of the zone, injecting cold liquid normally gaseous hydrocarbon into said zone at spaced points along the length thereof to effect chilling of the oil mixture passing therethrough, the proportion of liquid normally gaseous hydrocarbon introduced at said points Ibeing such as to chill the oil mixture to progressively lower temperatures as it advances through said zone and to precipitate the wax content of the oil desired to be removed therefrom, maintaining a pressure in said zone sufficient to prevent vaporization of the injected chilling medium, withdrawing the resulting chilled oil mixture containing precipitated wax from the bottom of said zone, separating the precipitated Wax from the Withdrawn mixture, washing the separated wax' with an extremely cold liquefied normally gaseous hydrocarbon, and utilizing the resulting Wash liquid as the cold normally gaseous hydrocarbon injected into said zone.

DAVID G. BRANDT. 

